Field of the Invention
The invention relates to a polymer with electrical semiconductor properties, a method for producing such a polymer, and a semiconductor component containing such a polymer, and to a method for producing the semiconductor component.
Semiconductor chips have found widespread use in a variety of technical applications. But their fabrication remains a costly and intensive process. Silicon substrates can be thinned to very small layer thicknesses in order to be made flexible. However, these methods are likewise expensive. Therefore, flexible or bent microchips are suitable only for highly demanding applications in which higher costs can be accepted. Utilizing organic semiconductors makes possible a cost-effective fabrication of microelectronic semiconductor circuits on flexible substrates. For instance, one application is a thin film with integrated control elements for liquid crystal screens. Another field of application is transponder technology, where information about a product is stored on what are known as tags.
Organic semiconductors can be easily structured by printing processes, for instance. However, the application of these organic semiconductors is still limited at present by the low mobility of the charge carriers in the organic polymer semiconductors. This presently stands at 1 to 2 cm2/Vs at most. The maximum working frequency of transistors, and thus of the electronic circuit, is limited by the mobility of the charge carriers (holes or electrons). Mobilities on the order of 10−1 cm2/Vs are sufficient for driver applications in the fabrication of TFT active matrix displays. Organic semiconductors are not yet suitable for high-frequency applications. A wireless information transmission (RF-ID systems) can only be achieved above a defined minimum frequency for technical reasons. In systems that draw their energy directly from the electromagnetic alternating field and that, therefore, lack their own voltage supply, carrier frequencies of 125 kHz and 13.56 MHz, respectively, are common. Such systems are utilized for identifying or marking objects in smartcards, ID tags, or electronic postage stamps, for example. Methods in which semiconductive molecules such as pentazane or oligothiophene can be deposited optimally systematically have been developed for the purpose of improving the charge carrier transport in organic semiconductors. This can be achieved by vacuum sublimation, for example. Systematic depositing of the organic semiconductor increases the crystallinity of the semiconductor material. The energy barriers for the charge carrier transport can be lowered by the improved—overlap between the molecules, i.e. between the side chains. By substituting blocking groups for the semiconductive molecule units, domains with liquid-crystalline properties can be generated in the deposition of the organic semiconductor from the liquid or gas phase. Beyond this, synthesis techniques have been developed in which an optimally high regio-regularity is achieved in polymers through the utilization of asymmetrical monomers.
Electrically semiconductive polymers are needed in field effect transistors or electronic components based on a field effect. This type of configuration is described in M. G. Kane et al., IEEE Electron Device Letters, Vol. 21, No. 11 (2000), p. 534; or D. J. Gundlach et al., 1999 International Electron Devices Meeting (December 1999)
In order to apply organic polymers in field effect transistors or similar electronic components, the polymer must behave like an insulator when there is no electrical field, and must exhibit semiconductor characteristics, forming a conduction channel, under the influence of an electrical field. Polyphenylenes or polynaphthaline derivatives have such properties. But these are not processible owing to their insolubility, which means that field effect transistors cannot be fabricated with these compounds.